Control for fluid servo actuated valve



@et E, 3956 G. F. BRAKE 4 2955,30@

CONTROL FOR FLUID sERvo ACTUATED VALVE:

Filed March 28, 1952 m ss d Y n CONTROL FR FLUID SERVO ACTUATED VALVEGeorge Forrest Drake, Rockford, Ill., assignor to Woodward GovernorCompany, Rockford, iii., a corporation of Illinois Application March 28,1952, Serial No. 279,080

3 Claims. (Cl. 137-26) This invention relates to fluid pressure systemsincluding a iluid ow control valve and a iluid actuated servo thereforselectively energized by a condition responsive device to vary the fluidflow through the valve.

One object is to provide a new and improved means for proportioning theflow of iluid through the main valve accurately in proportion to changesin the position of the movable valve member while at the same timepermitting adjustment of the valve position for a given condition of thecondition responsive device.

Another object is to automatically maintain a predetermined pressuredierential across said main valve in a novel manner and selectivelyadjust the amount of said diierential to modify the action of the valve.

A further object is to adjust said pressure differential automaticallywith changes in the control point of the condition responsive device bywhich the main fluid servo is energized.

Other objects and advantages of the invention will become apparent fromthe following detailed description taken in connection with theaccompanying drawing which is a schematic view and hydraulic circuitdiagram of a uid servo system embodying the novel features of thepresent invention.

For purposes of illustration, the invention is shown in the drawingincorporated in a system for varying the energization of a fluidpressure servo 11 automatically in accordance with changes in acondition such as speed and correspondingly regulating the ow ofpressure uid through a valve l to a point of use through a passage 9.The valve and the ports governing its operation are housed within acasing 12, the valve shown comprising a plunger 15 having spaced lands16 and 17 thereon slidable in a bore 18. The land 16 coacts with anoutlet port 19 which is generally V-shaped to effect a uniform change inthe ow through the valve for each increment of plunger movementthroughout the full range. Liquid from a suitable source is supplied tothe inlet 20 of a power driven pump 21 which may be of the gear typewith its outlet connected to a passage 22 leading into the bore 1Sbetween the valve lands.

The servo 11 for actuating the valve 10 comprises a piston 23 fast onthe valve member 16 and slidable in a cylinder 24. Herein, the piston isbiased in the valve closing direction by pressure from a supply line 25acting on the end of a piston 26 rigid with the piston 23 and slidablein a cylinder 27 substantially smaller in size than the piston 23. Fluiddelivered by the pump 21 is supplied to the line 25 through a passage 28and an .automatic regulating valve .29 loaded by a spring 30 and actingto maintain the pressure in the line 25 at a constant value.

Energization of the servovis varied by controlling the pressure on thelarger end of the piston 23 by admitting fluid from the line 25 to thecylinder 24 or by releasing iluid from the cylinder to a drain-passage31. While Vsuch flow -of the uid lmay be controlled Vautomatically inrespouse to changes in any electrical, physical, or chemical condition,the control shown herein for purposes of illusrates atent i trationcomprises a governor 32 sensitive to changes in speed for example, thatof a prime mover supplied with fuel delivered through the valve 10. v l

The governor 32 may be of the construction disclosed in Patent No.2,478,753 which may be referred to for further details. The speed senserof the governor corri` prises a pair of flyweights 33 pivoted on a ballheady 34 in the form kof a gear which is fast on the upper end of aported sleeve 35 rotatable in a bushing supported in the casing 12. Theball head is geared or otherwise suitably coupled to a source of rotarypower whose speed is to be sensed. l

The centrifugal force acting on the yweights is balanced against acompression spring 36 bearing downwardly on the arms of the yweightsthrough a ball thrust bearing 37. The speed setting of the governor maybe adjusted manually by turning a shaft 38 jour naled in the casing 12and carrying a selector arm 39. A cam 40 fast on the shaft acts on aslidable plunger 4l whose motion is transmitted through a lever 42fulcrtuned at 43 to a plunger 4.4 slidable in a bore 45 and abuttingagainst the upper end of the Speeder spring 36 which is compressed andextended as the selector 39 is turned counterclockwise and clockwiserespectively to increase and decrease the speed setting.

The control force derived from changes in the yweight .speed is appliedto a plunger 46 of a pilot valve 47 formed by a port 48 coacting with aland 49 on the plunger. The latter is slidable in the sleeve 35 and isconnected at its upperend to the upper race of the bearing 37. Below theland 4,9, the sleeve 35 communicates with the drain passage 311. Througha hole in the sleeve 35 the pressure supply line 25 communicatescontinuously with the space above the valve land. The voutlet port 4S isconnected to a passage 50 communicating with one end of a cylinder 5 1having a `piston 52 slidable therein and lurged toward a centeredposition by compression springs 5,3 Vand 5 4. The other end of thecylinder communicates through a passage 55 with the upper end of theservo cylinder 24 so that pressure uctuations in the ,passage 50 arecommunicated to the top of the servo piston 23 through the intermediaryof the piston 52.

A compensating system for lproducing isochronous operation of thegovernor 32 :includes a piston 56 `fast on the valve stern 46 andreciprocable in a cylinder 57 connected at its lower end to the valvecontrolled passage 50. A passage k.58 extends from the upper end of thecylinder 57 to the passage' 55 and the servo cylinder 2,4. A by-passage59 having a needle valve 60 therein permits slow leakage of fluidbetween the passages 50 and 58. As more fully described in the aforesaidpatent, lowering of the land 49 below its neutral position opposite theport 4S in response to a speed decrease ybelow the Vprevailing settingof the governor results in forcing fluid into the servo cylinder 24 thuscausing the piston 23 to be moved downwardly. Conversely a detected risein speed causes the valve land to be raised above the port 48 allowingiluid to escape to the drain thus decreasing pressure in the passage 50which allow-s the piston 23 to move under its constant bias in the valveclosing direction.

To proportion the fluid ow accurately in `accordance with changes in theposition of the valve plunger 16, Vthe excess of the uid delivered byVthe pump 21 is by-passed back to the pump inlet 20 automatically underthe control of a valve 60 which responds to the pressure drop across themain valve 10 and operates automatically in conjunction with a pressureresponsive pilot valve 61 to maintain this drop constant within veryclose limits. For this-purpose,fthe byfpassvalve 60 comprises a land 62slidable in a bore 63 and cooperating with a port 64 which communicateswith a return or by-passage 65 leading to the pump inlet. The pumpoutlet 21 communicates continuously with the bore 63 at a point betweenthe land 62 and a piston 66 connected to the land by a plunger 67 andalso slidable in the bore.

The plunger is urged by a compression spring 68 in a direction to closethe by-pass valve 60 and is shifted in the other direction by a servoactuator 69 formed by the piston 66 and the cylinder 63 and variablyenergized under the control of the pilot valve 61 which is sensitive tochanges in the pressure difference between the inlet and outlet passages22 and 9 of the main fuel valve 10. To this end, the servo cylinder 63beyond the outer end of the piston 66 communicates through a passage 74with a port 75 which opens into a cylinder 76 in which slides a plunger77 having spaced pistons 78 and 79 thereon. Opposite ends of thecylinder 76 are connected through passages 80 and 81 to the main valvepassages 9 and 22, there being a pressure reducing restriction 82 in theformer to permit the pressure in the outer end of the cylinder 76 to bereduced by the use of a relatively small relief valve 70 describedlater. A passage 83 leads from the intermediate portion of the cylinder76 to the iluid return line or pump inlet 20.

When the supply pressure acting on the piston 78 just balances thecombined force of a compression spring 84 and the pressure in the iluiddelivery passage 9 both of which act on the piston 79, the piston 78will be centered and the port 75 will be covered by the piston 78 asshown in the drawing, If the supply pressure increases above this value,the plunger 77 will be forced to the right admitting high pressure iluidthrough the port 75 and the passage 74 to the cylinder 63, and theincreased force thus acting on the piston 66 will force the plunger 67to the left and by-pass to the pump inlet 20 a greater part of the uiddelivered by the pump 21. Conversely, if the difference between thesupply and delivered pressures decreases below the desired value, thepilot plunger 77 will be moved to the left uncovering more of the port75 and permitting fluid to escape from the cylinder 63 so as to reducethe force on the servo piston 66 and initiate closure of the valve 60.The amount of the by-pass is thus reduced until the proper pressuredifferential across the main valve is again attained.

if, for any reason, the pressure in the delivery line 22 ever exceeds asafe value, an adjustable spring loaded check valve 7i) communicatingwith the valve outlet 81 opens admitting pressure fluid through the line74 to the piston 66 of the regulating valve 60. The increased pressureon the latter moves the plunger 67 to open the valve 60 thereby causingthe pressure differential across the valve 10 to drop. The plunger 77 ofthe valve 61 is thus allowed to move to the left. Fluid is thuspermitted to drain out through the port 75 and a restriction 71 whichlimits the flow until the abnormal pressure has been relieved.

By utilizing the pilot valve 61 in the manner described above,deviations in the pressure drop across the valve 10 from the valuedesired are sensed without actual movement of the by-pass valve plunger67 and the energization of the servo 69 is changed correspondingly. EX-tremely close regulation of the pressure drop across the valve is thusattained so that the rate of fluid flow always corresponds accuratelywith the position of the valve member 16.

In accordance with one aspect of the invention, advantage is taken of acharacteristic of the pressure regulating system above described to varythe pressure which, for a F given value of the condition sensed by thecondition responsive device 32, is maintained in the delivery passage 9by the action of the servo 11 in adjusting the main valve 10. T o effectsuch adjustment, it is only necessary to vary the loading of the pilotvalve 61 as by angularly turning a cam 36 fast on a shaft 87 and actingon a follower 38 slidable through the end of the cylinder 76 and bearingagainst the outer end of the spring. The shaft is journaled in thecasing 12 and adapted to be held in different positions of adjustment bysuitable means. ln the present instance, the shaft is adjustable inpredetermined steps corresponding to tlat surfaces 89 spaced around theperiphery of the cam 86 and disposed at different distances from theaxis. The spring force acting through the follower and on one of theparts 89 of the cam thus holds the cam in the selected position.

By turning the cam to different positions, the stress of the spring 84may be adjusted thus varying pressure differential to which the valve 61responds and therefore the pressure drop across the valve 10.Accordingly, the ow of fluid through the delivery passage 9 for a givenposition of the valve may be adjusted as desired and independently ofthe action of the condition responsive device'32.

In automatic control systems of the above character, it is frequentlydesirable to vary the rate of uid delivery through the passage 9 inaccordance with changes in the setting of the Icontrol :point of thecondition responsive device 32. This may be accomplished conveniently byvarying the loading of the pil-ot valve 61 with changes in the positionof the shaft 38 by which the speed setting of the governor 32 isadjusted. As an `example, let it be assumed that the pressure dropacross the valve i10 is to be reduced progressively as the selector 39is turned `in the speed decreasing direct-ion below a predeterminedspeed value. For this purpose, this movement of the selector "39 isutilized to increase the loading imposed on the pressure sensing pilotvalve 6l by a spring -91 acting in opposition to the main loading spring84 of this valve. Herein, the spring 91 is of the compression type andis arranged within the cylinder 76 with one end abutting against ytheland 78 and the other end engageable with an .abutment 92 on a rod 93which .slides throu-gh the .end of the cylinder 76 for engagement withthe end of a screw 94 threaded through the free end of .an arm 95. Thelatter is fast on the selector shaft 38 and positioned for engagement oflthe screw 94 with the end of .the rod 93 when the selector, in movingin the speed decreasing direction, moves beyond a predeterminedposition. ln this movement, fthe abutment 92 is moved away from itsnormal position against the end of the cylinder 76, and the force of thespring 911 is increased thus reducing the resultant leftward lforce onthe plunger 77 by which force the maintained supply pressure isdetermined. The pressure drop across the valve 10 is reducedcorrespondingly thereby decreasing the amount of fluid which flowsthrough the valve when the auXil-iary loading spring 91 is active, Theamount of the decrease in the supply pressure .increases as the shaft 38is turned further in the clockwise direction.

If desired, the flow of iluid through the valve 10 may be cut offcompletely by continuing the clockwise turning of the selector shaft 3Sbeyond the position in which the extended inner end '96 of the rod 93engages the pilot valve -plunger 77. The latter is thus shifted to thenight fully opening the relief valve 61. This drops the pump dischargepressure to the lowest possi-ble value when the pump 21 is operating andthe valve 10 is closed I claim as my invention:

l. In a system of the character described, the combination of, a sourceof fluid under pressure, a main valve controlling .the flow of iluidfrom said source and having an inlet and an outlet and a member movableto vary the uid flow therebetween, 'a iiuid servo for positioning saidvalve according to the degree of energization of the servo, conditionresponsive mechanism operable selectively to control the admission offluid from said source of said servo, Aan adjuster selectively movableto different positions to vary the control point of said conditionresponsive means, a second valve regulating the pressure of said uid insaid inlet, a uid actuator for positioning said second valve inaccordance with the energization of said actuator, means including athird valve controlling `the ow of fluid from said inlet to saidactuator and having a piston responsive to the pressures in said inletyand said outlet whereby to vary the energization of said actuator andmaintain a predetermined pressure difference between said inlet andoutle-t, -a spring for loading said piston and selectively adjustable tovary the force acting on the piston, and mechanism movable by saidadjuster to change the force exerted by said spring on said piston.

2. In a system of the character described, the combination of, a sourceof fluid under pressure, a main valve controlling the tiow of fluid fromsaid source and having an inlet und an outlet .and ya member movable tovary the uid ow therebetween, a iiuid servo for positioning said valveaccording to the degree of `energ-ization of lthe servo, conditionresponsive mechanism operable selectively to control the admission offluid from said source to said servo, an adjuster selectively movable todiierent posi-tions to vary the control point of said conditionresponsive means, a second valve regulating the pressure of said fluidin said inlet, `a `-fluid actuator for positioning said second valve inaccordance with the energization of said actuator, means including athird valve ycontrolling the tiow of uid from said inlet to saidactuator and having a piston responsive to the pressures in said inletand said outlet whereby to vary the energization of said actuator andlmaintain a predetermined pressure diterential between said inlet andoutlet, and a connection between said adjuster and said piston includinga spring and an `adjust-able lost motion device and operable .after theslack in said device has been taken up to transmit the movements of theadjuster to said piston to vary the force exerted thereon.

3. In a system of the character described, the combination of, a sourceof fluid under pressure, a main valve controlling the ow of tluid fromsaid source and having an inlet and an outlet and a member movable tovary the uid ow therebetween, a uid servo for positioning said valve.according to the degree of energization of the servo, conditionrespon-sive mechanism operable -selectively to control the admission offluid from said source -to said servo, an Iadjuster selectively movableto different positions to vary the cont-rol point of said conditionresponsive means, 4a second valve regulating the pressure of said uid insaid inlet, a iiuid .actuator for positioning said second valve inaccordance with the energization of said actuator, means including athird valve controlling the liow of iluid from said inlet to saidactuator and having a .piston responsive to the pressures in said inletand said outlet whereby to vary the energization of said actuatormaintain `a predetermined pressure `differential between said inlet andoutlet, a spring for exerting supplemental loading force on said piston,and a iconnection for transmitting the movement `of said adjuster tosaid spring to vary the force exerted on the piston.

References Cited in the file of this patent UNITED STATES PATENTS1,538,427 Earl May 19, 1925 1,904,475 Kissing u Apr. 18, 1933 2,102,865Vickers Dec. 21, 1937 2,422,808 Stokes c June 24, 1947 2,478,753 ParkerAug. 9, 1949 2,581,275 Mock Jian. l, 1952 2,6l\6,507 Greenland Nov. 4,11952 FOREIGN PATENTS 634,095 Grenat Britain Mar. l5, 1950

